Volvo Penta D2-40 max alternator size

[Gonaboat]

Hello, My new to me boat has a VP D2-40 and will need an alternator upgrade to cope with charging a lithium bank of 400Ah



My previous boat had a Yanmar 2gmf20 and i had fitted a Balmar 90amp alternator to it. This in the real world was a little big for the engine and it would bring down the RPM significantly when parking in marinas if the batteries were taking full charge.


Ideally i would like to fit a Balmar XT 170amp alternator to the D2-40. Knowing that this style alternator puts out close to its stated amps for an hour or more with Lithium setups has anyone had some real life experience of fitting this size alternator to a D2-40 and and any pitfalls or issues experienced. Its a very common engine so i dont want to try and reinvent the wheel!

[SV_FlyingTigress]

I Have 2x 2016 D2 40-F. One has the original 115A alternator that was changed to externally regulated and the other has the 250A Balmar all connected with a center-fielder unit (which I found so problematic that I have since disabled it). I found that when I purchased the Balmar that that vendor indicated they definitely had a unit that would work with my engine, which I bought. They didn't indicate that, while it would take a change over to serpentine belts (to give traction to drive the additional drag producing the rated amps), that the *pulley* kit was no longer carried for the D2-40* and was not (apparently) otherwise commercially available. I called the gentleman (now deceased I understand, RIP) that made the custom pulley kits for the D2-40 and he indicated that he would need about $3K+ US to make them and that they *should* work. So my solution was to find a narrower J(8?) serpentine pulley that would work, setting the belt tension high and using the electronically configurable clutch function in the Balmar controller to derate the 250A alternator down to producing about 1508Watts/12V .... any higher than that an it would slip...so now it is producing just over 100A when you do the division with charging voltage of over 13V... SO, unless you own a machine shop with a big lathe to make your own pulleys......my advice for your model of engine is 1) consider just externally regulating stock (115A?) alternators or 2) Avoid the huge Balmar alternators unless you first... 3) Solve your pulley conversion before you consider alternators and when you have that dialed, then determine which alternator you can fit. If you want to go around 150A in alternator size, figure out how to get (minimally) a J10 fully set installed and tested, if 200A or more, figure out how to get J12 groove pulleys/bell installed and tested first. I think the D2-40 would drive the 250A (bigger than you need with your stated battery bank) if it had J12 (12 groove) pulleys and a quality belt. If you do solve the pulley situation and they accidentally make a spare set, I can tell you where to send them.. hopefully I just saved you quite a few thousand.

[Gonaboat]

Thanks for the comprehensive real world reply.


It would look like i may be in luck in that the engine seems to have been fitted with a serpentine belt from new but maybe not as wide as needed. I will need to check what size it is when i get down to the boat.


Gordon